>. 
Beane le 
W. S. Sullivant on Nobert’s Test-plate. 349 
correspond with the registration on the test-plate (p. 100), 
challenges the admiration of all interested in microscopy, an 
proves by the inexorable test of experiment, that the resolution — 
of such lines is not incompatible with the physical properties 
of light, as has been asserted by Fraunhofer and other writers 
of authority on optics. 
e grade of some of the objectives with which these reso- 
lutions were made is scarcely less remarkable than the resolu- 
tions themselves. Reliance was placed, not so much on those 
beautiful achievements in optical art, the ; and the ,'; lately 
sent out by Powell and Lealand, as on objectives of a medium 
grade, such as a + ¢mmersion and a1 dry by Tolles. Mr. Stodder 
says “these trials show conclusively that it is not the great 
power of the objective that is important, for in many of the 
trials here reported, the lower powers have given the best re- 
sults, but the skill of the opticians in making the instrument.” 
The objectives of Mr. Tolles unquestionably rank among the 
st, but it may be doubted if evidence exists, unless it be these 
trials reported by Mr. Stodder, of their superiority to those 
e by Spencer in this country, and by Powell and Lealand 
and others in England. Hence it is a fair inference that the 
failure of previous efforts on the highest bands of the Nobert 
tes!-plate is attributable to causes other than an incapacity In 
the objectives used. 
. Stodder would have done an acceptable service to those 
who may hereafter attempt such investigations, had he gone 
Somewhat into detail as to the system of illumination, the aux- 
apparatus, &c., adopted by himself and other gentlemen 
whose experiments he reports. : 
Such success in carrying up the resolvability of lines so far 
beyond the point at which well-directed efforts, sustained by 
: n inch. ae 
. {tis well known to all familiar with this subject, that it 1s 
apossible to distinguish, by their mere visual appearance, the 
— from the true lines on the highest bands of the Nobert 
eeutnted, measured, and found to correspond with the regis- 
aioe. on the test-plate.* a 
ea here assumed that the lines are ruled on the test-plate a8 indicated by 
— i lates. 
. 
having yet been found on any of his p: 
